1. Field of the Invention
The present invention generally relates to a gas analyzing method for a semiconductor treater, and more specifically, it relates to a gas analyzing method for a semiconductor treater so improved as to monitor leakage or change of gas composition influencing the treatability of the semiconductor treater employing a vacuum in situ for improving the productivity and the reliability of the semiconductor treater. The present invention also relates to a gas analyzer for a semiconductor treater capable of implementing such a method.
2. Description of the Background Art
A semiconductor treater is now described with reference to a plasma treater such as a dry etching apparatus (hereinafter referred to as an etching apparatus), for example, treating a semiconductor wafer (hereinafter referred to as a wafer) with a plasma.
The etching apparatus introduces treating gas into a plasma treatment chamber (hereinafter referred to as a chamber) set to a vacuum atmosphere for generating a plasma thereby forming chemically active ions and radicals (neutral active species) by ionization or dissociation of the treating gas. The ions and radicals physically or chemically act to etch a desired portion of a treated film provided on the wafer for forming a desired device pattern.
At this time, leakage to the outside air takes place in a vacuum sealing part of the chamber or a treating gas supply system, such that atmospheric components are mixed into the treating gas or the flow rate of the treating gas or the like is changed by some cause. In this case, the compositions of the ions and radicals contained in the plasma are so changed that no desired etching characteristic is attained but the reliability and the productivity of a semiconductor device are remarkably inhibited.
In general, therefore, pressure change is checked with a vacuum meter, emission of the plasma is analyzed, or a helium leak detector or a mass spectrometer is employed for analyzing the gas in the chamber.
However, in the method employing a vacuum meter, for example, it is difficult to sense slight leakage due to low sensitivity, although pressure increase resulting from leakage can be sensed. Further, this method is inferior in reliability due to change of the sensitivity of the vacuum meter caused by a reactive plasma or insufficient reproducibility. Further, it can be said substantially impossible to analyze the gas species in this method in principle.
Japanese Patent Laying-Open No. 02-82131 (1990) discloses a method of checking leakage with a helium leak detector. However, the measurer employed in this method is relatively high-priced although the same has high sensitivity. Further, He gas must be supplied around the chamber or the like, and an He gas spray must be mounted on a vacuum pumping system of the apparatus for making an inspection. In addition, this method cannot make measurement during etching, and cannot analyze gas species.
A mass spectrometer such as a quadruple mass spectrometer (Q-Mass) is capable of highly sensitive gas analysis, leakage check and in-situ monitoring during etching. However, the mass spectrometer is disadvantageously high-priced. Further, the sensitivity of the mass spectrometer is remarkably changed due to contamination of a measuring electrode or an ionization filament with a reaction product formed during etching, deterioration by an active plasma or the like, and only a qualitative result can be obtained. Further, metal contamination may be caused on the wafer with an electrode material.
Japanese Patent Laying-Open No. 61-97928 (1986) proposes a method of identifying gas species by analyzing radicals and ions contained in a plasma employed for treating a wafer through emission of the plasma. This method enables highly sensitive in-situ monitoring. Further, this method causes no influence such as metal contamination on the process due to optical observation through a window formed on a chamber wall. In addition, atmospheric leakage can be checked by detecting the emission spectrum (335 nm, 674 nm or the like) of nitrogen contained in the atmosphere. In this method, however, the emission strength is inevitably reduced by hazing of a measuring window provided on the chamber resulting from a reaction product formed during etching. Thus, periodic cleaning must be inevitably performed for preventing reduction of detection sensitivity. Further, the emission spectrum of nitrogen or oxygen employed for leakage check may frequently overlap with the emission spectrum of a treated plasma depending on the type of the treating gas, and it is difficult to apply this method to a recent etching apparatus employing various types of gas. Further, the gas analyzing method employing emission spectroscopy can be executed only during plasma generation (treatment) as a matter of course, and cannot be applied to an apparatus utilizing no plasma.
In addition, the species of gas having no emission spectrum data cannot be identified, as a matter of course. Even in gas having a known emission spectrum, the strength of the spectrum may change or overlap with the spectrum of another gas to cause difficulty in identification of the gas species depending on mixed gas or discharge conditions.